WASHINGTON — The Environmental Protection Agency announced Thursday that it suspects hydraulic fracturing in a shallow natural gas well in Wyoming contaminated a town’s drinking water. After three years of study, the agency concluded that chemicals found in the aquifer and in individual wells were consistent with those used in hydraulic fracturing.

The agency issued a report that will be open for public comment and scientific review. If it is finalized with the same conclusions, it could provide the first documented case in which “fracking” contaminated groundwater.

“Alternative explanations were carefully considered to explain individual sets of data,” the draft report says. “However, when considered together with other lines of evidence, the data indicates likely impact to ground water that can be explained by hydraulic fracturing.”

Inhofe comments

Sen. Jim Inhofe, R-Tulsa, said the agency’s findings were premature and political, while an environmental group called the study “a huge blow to the oil and gas industry.”

Hydraulic fracturing, which has been used for more than 50 years on oil and gas wells, involves pumping water, sand and a small amount of chemicals into a well to create cracks in shale formations.

The process, in tandem with horizontal drilling, has been used increasingly by the industry to produce oil and gas that was previously considered too difficult to recover. It has come under increasing scrutiny and criticism as its use has expanded, and some have charged that it poses a threat to groundwater.

Though there have been incidents in which “flowback” water used in a well was improperly handled, the industry has countered criticisms of hydraulic fracturing by saying there had not been a documented case in which the process itself caused contamination.

The EPA study in Pavillion, Wyo., began in 2008 after residents complained that their water smelled and tasted bad. The residents lived near a gas field controlled by Encana, a Canadian energy company.

According to the EPA, the agency constructed two monitoring wells to sample water in the aquifer.

“EPA’s analysis of samples taken from the agency’s deep monitoring wells in the aquifer indicates detection of synthetic chemicals, like glycols and alcohols consistent with gas production and hydraulic fracturing fluids, benzene concentrations well above Safe Drinking Water Act standards and high methane levels,” the agency said in a statement.

Contaminants migrate

“Given the area’s complex geology and the proximity of drinking water wells to ground water contamination, EPA is concerned about the movement of contaminants within the aquifer and the safety of drinking water wells over time.”

Water in private wells tested by the EPA contained compounds “consistent with migration from areas of gas production,” the agency said.

The Environmental Protection Agency noted, however, that the fracturing in Pavillion is taking place “in and below the drinking water aquifer and in close proximity to drinking water wells — production conditions different from those in many other areas of the country.”

Industry experts have often said that most fracturing occurs a mile or more below the surface, while groundwater is close to the surface, and that there is no way that fracking water or gas could migrate to drinking water from those depths.

Inhofe has been of the most vocal defenders in Congress of hydraulic fracturing and has been following the EPA’s work in Pavillion and its national study of fracking. Thursday he said the EPA draft report was part of President Barack Obama’s “war on fossil fuels.”

“EPA’s conclusions are not based on sound science but rather on political science,” Inhofe said.

“Its findings are premature, given that the agency has not gone through the necessary peer-review process, and there are still serious outstanding questions regarding EPA’s data and methodology.”

Wenonah Hauter, executive director of Food and Water Watch, said the draft report “illustrates the dangers of moving forward with a technology before we know the facts. It is also a huge blow to the oil and gas industry, who has continued to insist that fracking is safe.”

A 30-day peer-review process led by a panel of independent scientists also will be conducted.